set default size for embedded SVGs

many templates fail to set proper sizes for admin icons etc. This will
prevent SVGs from blowing up by default - of course templates should
still overwrite this default.

lib/styles/all.css

@@ -70,3 +70,8 @@ em em.u {
 img.icon.smiley {
     height: 1.2em;
 }
+
+svg {
+    width: auto;
+    height: 1.2em;
+}